vi Preface 



No attempt has been made to include the whole of the 

 fields represented by the general topics. The plan was to 

 select certain representative investigators to speak of their 

 work. Four such investigators were selected, the mission 

 of the fifth lecturer being to give the elementary information 

 (chaps, i and ii) necessary for an audience untrained in biolog>^, 

 and thus to prepare the way for the more special topics. 



It is hoped that similar series of lectures in other fields 

 of biology will be given during successive summers, and 

 that the present volume may be the first of a series which will 

 represent the most significant aspects of current biological 

 investigation. 



J. M. Coulter 



F. R. LiLLIE 



W. L. Tower 



